[pxe] Fix a typo in PXENV_GET_CACHED_INFO that broke Altiris

__from_data16 takes the value pointed to, rather than the pointer
itself.  This was silently causing gPXE to return a dud buffer pointer
when the caller did not supply a buffer for PXENV_GET_CACHED_INFO.

src/interface/pxe/pxe_preboot.c

@@ -197,7 +197,7 @@ PXENV_EXIT_t pxenv_get_cached_info ( struct s_PXENV_GET_CACHED_INFO
 		 */
 		get_cached_info->Buffer.segment = rm_ds;
 		get_cached_info->Buffer.offset =
-			( unsigned ) ( __from_data16 ( info ) );
+			( unsigned ) ( & __from_data16 ( *info ) );
 		get_cached_info->BufferSize = sizeof ( *info );
 		DBG ( " returning %04x:%04x+%04x['%x']",
 		      get_cached_info->Buffer.segment,